A prime mover or power drive device has been used extensively in the past to provide incremental or intermittent motion to more than one operating member, the purpose being to share a common driver both apparatus-wise and time-wise. In the case of an electric motor, either A C or D C, the motor may be of the continuous run type and engaging and disengaging means, in the nature of a combination of clutches and brakes, are positioned in the drive train to provide the desired motion. In this respect, the clutch or clutches engage the rotating drive to direct the motion to the operating apparatus or members, and then the clutch or clutches are made to be disengaged from the rotating drive, with the brake or brakes being utilized to rapidly decelerate and to stop driving motion to the operating members. In this approach, the clutch always is engaged with and disengaged from a dynamic or moving drive line, with the brake being likewise used in a dynamic manner. In other instances, a prime mover of the stepping type may also be used to provide incremental motion to the operating members.
While the closed loop control mode having a switching amplifier and a feedback circuit with pulse width modulated signals is representative and common in the art, certain improvements are being sought in the overall system to provide faster and more efficient equipment.
Representative of prior art in the area of the present invention is U.S. Pat. No. 2,929,268 to J. A. Ferro et al. which discloses a bi-directional incremental drive mechanism for use in servo systems and which includes drive and driven shafts with friction clutches and pawl and cam arrangements in the drive train. A continuously running motor is connected to the driving shafts which are rotatable in opposite directions and the friction clutches connect the driving and driven shafts. The pawl and cam arrangements enable advanced and retracted positions, the driven shafts being free to rotate in the pawl retracted position, and the pawls being normally biased in the advanced positions and responsive to servo signals for actuation to temporary retracted positions.
Another example of prior art is U.S. Pat. No. 3,667,383 to R. H. Mack et al. which discloses a print and transport belt synchronizer for a printer having a continuously rotating print drum and a control system including a pair of timing discs, one disc indicating the angular position of the drum and the second disc operating to signal the hammer carrier to engage the transport belt, there being a double-ended transducer responsive to the timing discs to provide appropriate signals for the printer.